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author | Eli Friedman <eli.friedman@gmail.com> | 2008-02-12 12:08:14 +0000 |
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committer | Eli Friedman <eli.friedman@gmail.com> | 2008-02-12 12:08:14 +0000 |
commit | 350307faa8002cd91c610d0dcd98f7b443b4a889 (patch) | |
tree | e178757efa27a2ea479122ee71c0c868342dc981 | |
parent | a5aa360d3ef8e21c51b6e7286b343d4fbe7ea4a6 (diff) | |
download | external_llvm-350307faa8002cd91c610d0dcd98f7b443b4a889.zip external_llvm-350307faa8002cd91c610d0dcd98f7b443b4a889.tar.gz external_llvm-350307faa8002cd91c610d0dcd98f7b443b4a889.tar.bz2 |
Fix for bug 1996: optimize out loads of undef. This code basically just
checks for a malloc/alloca immediately followed by a load.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47006 91177308-0d34-0410-b5e6-96231b3b80d8
-rw-r--r-- | lib/Transforms/Scalar/GVN.cpp | 29 |
1 files changed, 28 insertions, 1 deletions
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp index 42d7a93..69f0690 100644 --- a/lib/Transforms/Scalar/GVN.cpp +++ b/lib/Transforms/Scalar/GVN.cpp @@ -1010,7 +1010,34 @@ bool GVN::processLoad(LoadInst* L, dep = MD.getDependency(L, dep); } } - + + if (dep != MemoryDependenceAnalysis::None && + dep != MemoryDependenceAnalysis::NonLocal && + isa<AllocationInst>(dep)) { + // Check that this load is actually from the + // allocation we found + Value* v = L->getOperand(0); + while (true) { + if (BitCastInst *BC = dyn_cast<BitCastInst>(v)) + v = BC->getOperand(0); + else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(v)) + v = GEP->getOperand(0); + else + break; + } + if (v == dep) { + // If this load depends directly on an allocation, there isn't + // anything stored there; therefore, we can optimize this load + // to undef. + MD.removeInstruction(L); + + L->replaceAllUsesWith(UndefValue::get(L->getType())); + toErase.push_back(L); + deletedLoad = true; + NumGVNLoad++; + } + } + if (!deletedLoad) last = L; |